Occurrence of paralytic shellfish toxins in Cambodian Mekong pufferfish Tetraodon turgidus: selective toxin accumulation in the skin.

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The toxicity of two species of wild Cambodian freshwater pufferfish of the genus Tetraodon, T. turgidus and Tetraodon sp., was investigated. Tetraodon sp. was non-toxic. The toxicity of T. turgidus was localized mainly in the skin and ovary. Paralytic shellfish toxins (PSTs), comprising saxitoxin (STX) and decarbamoylsaxitoxin (dcSTX), account for approximately 85% of the total toxicity. Artificially reared specimens of the same species were non-toxic. When PST (dcSTX, 50 MU/individual) was administered intramuscularly into cultured specimens, toxins were transferred via the blood from the muscle into other body tissues, especially the skin. The majority (92.8%) of the toxin remaining in the body accumulated in the skin within 48h. When the same dosage of tetrodotoxin (TTX) was similarly administered, all specimens died within 3-4h, suggesting that this species is not resistant to TTX. Toxin analysis in the dead specimens revealed that more than half of the administered TTX remained in the muscle and a small amount was transferred into the skin. The presence of both toxic and non-toxic wild specimens in the same species indicates that PSTs of T. turgidus are derived from an exogenous origin, and are selectively transferred via the blood into the skin, where the toxins accumulate.